Within- and between-zygosity variance in oral traits among US and Punjabi twins.

Cross-cultural comparison of twin variances reveals widespread heterogeneity among zygosities for dental occlusal traits, implying various biases in calculation of genetic variance or heritability estimates. These estimates are fairly robust for dental size traits, however. Differences in pattern between Punjabi (Northwest Indian) and American twins highlight the environmental differences that affect heritability determinations.